Lung cancer is the most common cancer worldwide, accounting for 1.3 million cancer deaths annually. Despite extensive efforts to elucidate mechanisms and develop new therapeutic regimens, the worldwide mortality rate of lung cancer remains high. Our long- term goal is to understand how mdig gene contributes to the initiation and progression of the human lung cancer and whether mdig can be served as a biomarker and a therapeutic target for lung cancer resulted from exposure to environmental or occupational hazards. The objective of this application is to investigate the role of Mdig protein played on the lung cell proliferation and carcinogenic transformation induced by environmental and occupational hazards/carcinogens. The central hypothesis is that Mdig promotes cell growth and transformation by functioning as a histone demethylase that antagonizes tri-methyl lysine 9 on histone H3. Down-regulation of tri-methyl lysine 9 of histone H3 will enhance the expression of genes associated with the cell cycle regulation and malignant transformation in lung epithelial cells. The rationale behind this proposal is that expression of mdig gene may be critical for lung cell proliferation and carcinogenic transformation in response to environmental carcinogens. To accomplish the objectives of this application, we will pursue three specific aims by using cell lines and nude mice as experimental models: (1) test the potential demethylase activity of mdig protein toward tri-methylated lysine 9 on histone H3; (2) determine whether the expression of the cell cycle-regulated genes, such as cyclins, Cdc25s and checkpoint proteins, is regulated by the methylation regulation of mdig; and (3) study the tumorigenic effect of mdig by both over- expression and down-regulation of mdig in BEAS-2B cells and A549 cells, respectively, in both cell culture and inoculation of the cells in nude mice. At the completion of these specific aims, we expect to have determined how mdig contributes to lung cell growth regulation and carcinogenic transformation in response to factors that cause lung cancer. We additionally expect, based on preliminary studies, that constitutive expression of mdig will compromise the tri-methylation of lysine 9 on histone H3, leading to attenuation of heterochromatin or the formation of other inhibitory epigenetic markers. As a result, the expression of genes associated with the cell cycle transition and cell proliferation will be enhanced. Finally, in addition to reveal a previously unknown new mechanism of the human lung cancer, it is anticipated that expression of mdig can be potentially served as a new biomarker and therapeutic target of the human lung cancer.